Project Summary The prevalence of food allergies has increased in the past several decades with an estimated 5% of children and 3-4% of adults in industrialized countries affected. Food allergies are defined by an adverse immune response following exposure to a given food and can manifest in symptoms ranging from localized itching, swelling and diarrhea to acute anaphylaxis. Currently, there are few available treatments to either prevent or cure food allergies, and available medications only treat symptoms following onset of the allergic response. Given the public health and economic impact of food allergies, there is an urgent need to identify new targets for the development of therapeutics for treatment, as well as potential diagnostic tools, to treat this debilitating condition. It is well-established that allergic diseases tend to develop in a sequential manner in childhood, a phenomenon referred to as the `atopic march'. This phenomenon commonly manifests as a child with atopic dermatitis going on to subsequently develop asthma, or allergic reactions to aeroallergens. In addition to asthma and allergic rhinitis, epidemiological studies have demonstrated that cutaneous inflammation associated with atopic dermatitis (AD) is a significant risk factor for the development of food allergies. In addition, animal studies using models of epicutaneous sensitization have demonstrated that this route of sensitization can predispose to antigen-induced allergic inflammation at other barrier sites. Taken together, these data indicate that the skin may be a highly relevant site of food allergen sensitization. However, the immunological mechanisms through which antigen sensitization in the skin can predispose to allergic inflammation in the intestine are unclear. It is becoming increasingly clear that cytokines produced by epithelial cells at barrier surfaces play an important role in shaping the responses to food antigens. These cytokines include TSLP, IL-25 and IL-33, which are expressed in coordinated fashion and have the ability to promote type 2 inflammatory responses through the activation of specific innate immune cell populations. Important for the work in this project, several studies have found that TSLP-mediated epicutaneous sensitization can exacerbate allergen-induced airway or GI tract inflammation, supporting a role for TSLP in the atopic march. We have established a model of food allergic responses in mice that allows us to perform epicutaneous sensitization in the presence of low levels of TSLP or IL-33, followed by oral challenge with the same antigen. Interestingly, it appears that IL-33 is critically important during both sensitization and oral challenge. We will use this model, in conjunction with samples from human patients with food allergies, to investigate the role of IL-33 in the loss of tolerance to food-related antigens (Aim 1), and determine whether polymorphisms in the IL-33 and IL-1RL1 correlate with allergic responses to food antigens (Aim 2).